Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery system having a plurality of cells electrically connected with each other because high output and large capacity is necessary for the medium- or large-sized devices. Pouch-shaped lithium-ion polymer batteries, which are widely used as unit cells of the medium- or large-sized battery system, have a size greater than that of interrelated batteries used in small-sized devices.
FIG. 1 is a typical view illustrating a method of manufacturing an exemplary pouch-shaped lithium-ion polymer secondary battery (hereinafter, sometimes referred to as a “large-capacity polymer battery”), which is used in a high-output, large-capacity battery system.
Referring to FIG. 1, the large-capacity polymer battery 100 is manufactured by mounting an electrode assembly 300, which comprises cathodes, separation films, and anodes, in a pouch-shaped battery case 200, which is made of a high polymer resin and aluminum laminate sheet, and coupling electrode leads 410 and 420 to the battery case 200 while the electrode leads 410 and 420 protrude outward from the upper end of the battery case 200. From the electrode assembly 300 extends electrode taps 310 and 320, which are coupled to the electrode leads 410 and 420, respectively. At the coupling area between the battery case 200 and the electrode leads 410 and 420 are disposed thin resin films 500, which prevent leakage of an electrolyte from the battery and prevent moisture contained in the air from being introduced into the battery while accomplishing electrical insulation of the electrical leads 410 and 420.
FIG. 2 is a partially enlarged view illustrating the coupling between the electrode leads and the battery case of the large-capacity polymer battery shown in FIG. 1.
Referring to FIG. 2, the cathode lead 410 and the anode lead 420, which are electrically connected to electrode assembly (not shown), which comprises the cathodes, the separation films, and the anodes, are mounted in a sealed fashion in the pouch-shaped case 200, which is made of the aluminum laminate sheet, while the cathode lead 410 and the anode lead 420 protrude outward from the upper end of the battery case 200. The resin films 500 are disposed between the battery case 200 and the electrode leads 410 and 420.
When the battery is manufactured, an upper end member 210 and a lower end member 220 of the battery case 200 are welded to each other at high temperature and high pressure. However, moisture contained in the air may be introduced into the battery case or the electrolyte may leak from the battery case through the gaps between the electrode leads 410 and 420 and the resin films 500 of the manufactured battery. As a result, the service life of the battery is reduced with the passage of time.
When the upper end member 210 and the lower end member 220 of the battery case 200 are welded to each other at higher temperature and higher pressure in order to solve the above-mentioned problems, the resin films may be melted, and therefore, the outer surface of the battery is contaminated, or the thin resin films are damaged, which accelerates the reduction of the service life of the battery. Alternatively, the predetermined areas of the surfaces of the electrode leads, to which the resin films are applied, may be treated using chromate. However, this chromate treatment causes environmental pollution due to heavy metals, and therefore, it is not desirable.
Consequently, the necessity of providing a new technology to solve the above-mentioned problems is highly requested.